1. Field of the Invention
This invention pertains to the field of isocyanurate catalysts. More particularly this invention relates to the use of alkali metal tertiaryamino dithiocarbamate salts as isocyanurate catalysts.
2. Description of the Prior Art
The use of catalysts in preparing isocyanurate foams via the polymerization of a polyol, polyisocyanate and optionally other ingredients in the presence of a blowing agent is well-known. The isocyanurate group formation catalyst is used to trimerize the isocyanate groups to form the isocyanurate linkages. The polyol essentially acts as a modifying or reactive plasticizing agent in the overall polymeric scheme since a polymer containing only isocyanurate groups is itself too friable. Thus, the isocyanurate foam contains both isocyanurate groups as well as urethane linkages, with said urethane linkages acting to plasticize the foam. Initially the reaction proceeds to give a urethane quasi-prepolymer containing active isocyanate groups which during the subsequent reaction time period trimerize to give a polymer rich in urethane linkages. Subsequently the excess isocyanate reaction to form isocyanurate groups which ultimately produces a methane modified polyisocyanurate polymer.
Depending upon process condition utilized, both rigid and flexible polyisocyanurate foams may be prepared as well as the semi-flexible and semi-rigid types. Some main uses of the resultant foam include those of thermal insulation, and as building materials and the like. Examples of some prior art isocyanurate foams and methods of preparation are described in U.S. Pat. Nos. 3,745,133; 3,644,232; 3,676,380; 3,168,483; and 3,519,950, to name a few.
A number of prior art polyisocyanurate catalysts are known. However, in many instances these catalysts suffer from one or more deficiencies. Particularly, while useful in promoting trimerization of the isocyanate groups of isocyanurate polymer unites the catalysts cause foam processing problems. Thus, in some instances such well-known catalysts as potassium octoate and potassium acetate catalysts are overly temperature dependent. Thus, an unduly rapid end -- cure is realized in some cases with such catalysts. That is, with a gradual rise in temperature, catalyst activity is increased in an excessive manner, making it difficult to properly control foam rise. Yet, in many cases, typified by slab formation, a uniform cure rate is particularly sought.
In other situations catalysts such as amine-type isocyanurate catalysts including amino hexahydrotriazines are unduly slow with respect to their reactivity rate resulting in a lagging end -- cure. As a result, the foam so cured is not sufficiently cured in time to properly handle. The soft green foam coming out of the machine will have a tendency to warp if, for example, panel board is being produced.
It would therefore be a considerable advance in the art if a new class of isocyanurate catalysts were discovered which overcomes the just discussed processing drawbacks whereby optimum foam cure rates could be achieved. It would be a further desirable achievement if such new class of isocyanurate chemical catalysts could be equally adopted in preparing isocyanurate foams useful as both rigid and flexible foams in making panels, slabs and spray foam.
It therefore is an object of the present invention to provide new isocyanurate catalysts. It is further an object of this invention to provide isocyanurate catalysts which can be utilized in preparing rigid, flexible, semi-rigid or semi-flexible isocyanurate foams. Another object of the present invention is to provide isocyanurate foams utilizing a new class of isocyanurate group formation catalysts. Finally, it is an object of the present invention to prepare modified polyisocyanurate foams which have suitable thermal stability, uniform cell structure, low friability, excellent adhesion and other sought-after properties, using a new class of isocyanurate catalysts.